Embodiments of this disclosure relate generally to semiconductor fabrication, and more particularly to a method and apparatus for reducing implant topography reflection effects.
In conventional methods of lithography patterning to a photoresist layer, light may be reflected by the topography of a substrate. For example, the presence of shallow trench isolation (STI) features within the substrate may cause such reflections. Reflected light may cause unintended variations in areas of the photoresist, such as critical dimension (CD) variations of photoresist features as compared to IC design layout features. Furthermore, implant topography reflection may induce photoresist line peeling or “trench scum.”
Photoresist regions that are defined as dark regions on a mask may be subject to a certain level of exposure due to reflected radiation. If the intensity of the reflected radiation is above a certain exposure threshold, a dark region could effectively become exposed. Dark regions that become exposed as a result of reflected radiation may be referred to as “reversed regions.”
The CD of a photoresist feature in a reversed region may vary locally. Accordingly, adjusting mask bias on a global basis cannot fix this issue, because the variation is not standard across the photoresist. This may be especially true with complicated layout designs that have complex topography. Furthermore, adding a global rule to enlarge smaller patterns is a feed-back compensation solution that requires a wafer-level check, and therefore is not adequate in all respects.
In other conventional methods of lithography patterning, a developable bottom anti-reflective coating (DBARC) layer is deposited on a wafer to prevent reflection. As described in U.S. Pat. No. 7,341,939 to Oweyang et al., a photoresist layer is deposited upon the DBARC layer and the wafer is selectively exposed to irradiation. Although, this conventional solution prevents topography reflection, it is not adequate in all respects.
Thus, there is a need for a method and apparatus for locally compensating CD variation caused by topography reflection.